A standard prior art electromagnetic actuator, hereinafter referred to as a “solenoid”, typically comprises an electrical coil wound on a hollow bobbin. A ferromagnetic pole piece and an armature are disposed within or proximate the bobbin, and the magnetic field generated by the coil when energized causes the armature to move axially of the coil toward the pole piece. The armature and solenoid housing are then specially configured for either push or pull solenoids. The position of the armature with respect to the pole piece when the solenoid is de-energized is provided by a biasing spring that drives the armature away from the pole piece.
A “push” solenoid includes a plunger portion extending from the armature (“plunger”) through the pole piece and terminating at a point outside the pole piece end of the solenoid. When the coil is energized, the armature moves toward the pole piece and the plunger pushes outwardly of the solenoid housing. A bias spring moves the armature away from the pole piece when the coil is de-energized, causing the plunger to retract. A “pull” solenoid on the other hand is closed at the pole piece end. An opening at the opposite end allows a plunger portion to extend outwardly from the solenoid housing. When the coil is energized, the armature moves toward the pole piece and the plunger is pulled inwardly of the solenoid housing. The bias spring moves the armature away from the pole piece when the coil is de-energized thereby causing the plunger to re-extend, outwardly.
In the solenoid art, it is known to employ a permanent magnet within an armature to bias the armature in one direction or the other, depending upon the polarity of the magnet, to enhance the pull force of the armature in the solenoid and to negate the need for a bias spring; see, for example, in U.S. Pat. No. 3,218,523.
It is also known to employ neodymium as the magnetic material in a solenoid armature; see, for example, U.S. Pat. No. 6,932,317.
What is needed in the art is a solenoid having an armature incorporating a permanent magnet, preferably made of a rare earth material such as neodymium, wherein the magnet may be selectively positioned within the length of the armature to pre-select between a push-type, a pull-type or a dual acting solenoid thereby readily converting the functionality of the solenoid.